The present invention relates to a sound absorbing material used for a muffler of an internal combustion engine, a muffler using this sound absorbing material, and a method for forming a sound absorbing layer of the muffler.
A muffler aiming at sound reduction of exhaust gas is arranged in an exhaust system of an internal combustion engine of an automobile.
A muffler uses a sound absorbing material for preventing high frequency sound, and that sound absorbing material is mainly made of glass fiber.
As to arrangement of the muffler, a sub muffler and a pre muffler are arranged on the downstream side of an exhaust emission purifier using a catalyst, and a main muffler is arranged on the downmost stream side. Such a sub muffler and a pre muffler may be positioned at a short distance from the exhaust emission purifier, and, in such a case, a high temperature of the exhaust gas or large pulsation may influence on the sub muffler or the pre muffler.
In the related art, therefore, it is general that stainless wool is wound around a porous exhaust tube of the sub muffler or the pre muffler and a sound absorbing material such as glass fiber is wound around the outer periphery thereof or internally filled.
Although the glass fiber used as a sound absorbing material accomplishes the quality which can withstand use in various temperature ranges, the resistance property with respect to acid things or alkaline things included in the exhaust gas is insufficient. The glass fiber may be, therefore, degraded/broken and emitted into the air together with the exhaust gas.
In view of the above-described problems, an object of the present invention is to provide a sound absorbing material which is superior in acid resistance, alkali resistance and sound absorbing qualities, a muffler using this sound absorbing material, and a method for forming a sound absorbing layer of the muffler.
To achieve this aim, a first aspect according to the present invention provides a sound absorbing material, wherein multiple pieces of basalt yarn obtained by dissolving basalt to be tuned into continuous fibers are bundled to be a bundled material by using a fiber bundling agent and the bundled material is fibrillated to be bulky.
A second aspect according to the present invention provides a muffler, wherein multiple pieces of basalt yarn obtained by dissolving basalt to be continuous fibers are bundled as a bundled material by using a fiber bundling agent, and a sound absorbing material obtained by fibrillating the bundled material to be bulky is provided on the outer peripheral portion of a perforated pipe.
A third aspect according to the present invention relates to a method for forming a sound absorbing layer using the above-described sound absorbing material, comprising the steps of: bundling multiple pieces of basalt yarn obtained by dissolving basalt to be continuous fibers as a bundled material by using a fiber bundling agent; forming a bulky sound absorbing material by fibrillating this bundled material; and forming a sound absorbing layer by arranging the sound absorbing material on the outer peripheral portion of a perforated pipe which constitutes the muffler.
Further, with respect to the third aspect, in the step for forming the fibrillated sound absorbing material, the bundled material may be supplied in a nozzle, compressed air may be blown into the nozzle and the bundled material may be unraveled by this compressed air to continuously form the fibrillated sound absorbing material by using the nozzle.
Furthermore, with respect to the present invention, in the step for arranging the fibrillated sound absorbing material on the outer peripheral portion of the perforated pipe, the sound absorbing material may be supplied on the outer periphery of the perforated pipe while rotating the perforated pipe around its axis so that the sound absorbing material is wound around the perforated pipe.
Moreover, with respect to the present invention, when supplying the fibrillated sound absorbing material on the outer peripheral portion of the perforated pipe, the sound absorbing material may be supplied to the perforated pipe while giving tension to the sound absorbing material by a tension roller.
A fourth aspect according to the present invention provides a method for forming a sound absorbing layer, comprising the steps of: bundling multiple pieces of basalt yarn obtained by dissolving basalt to be continuous fibers as a bundled material by a fiber bundling agent; forming a bulky sound absorbing material by fibrillating the bundled material; and forming a sound absorbing layer by inserting and filling the sound absorbing material into a space between an outer pipe and a perforated pipe constituting a muffler.